Heat treating method and apparatus



May9, 1967 H. SMITH, JR 3,313,017

' HEAT TREATING METHOD AND APPARATUS INVENTOR Horace L. Smith, Jr.

BY QM #4117614 ATTORNEYS May 9, 1967 H. L. SMITH, JR 3,318,017

HEAT TREATING METHOD AND APPARATUS Original Filed Jan. 29, 1963 2 Sheets-Sheet 2 N INVENTOR w Horace L. Smith, Jr.

ATTILORNEYS United States Patent 3,318,017 HEAT TREATING METHOD AND APPARATUS Horace L. Smith, Jr., Richmond, Va., assignor to Hupp Corporation, Cleveland, Ohio, a corporation of Virginla Confirmation of application Ser. No. 254,674, Jan. 29, 1 963. This application May 2, 1966, Ser. No. 547,128 6 Claims. (Cl. 34-114) This application is a continuation of application No. 254,674, filed January 29, 1963, which is now abandoned.

This invention relates to the heat treatment of webs and continuous sheets of material, and, more particularly, to the drying of continuous webs of materials such as paper, plastic films, and the like. For convenience, the principles of this invention will be developed by relating them to paper drying. It is to be understood, however, that the principles of this invention may equally well be applied to the drying or heat treating of other, diverse types of web or continuous sheet materials including but not limited to those mentioned above. The term sheet will be hereinafter used to include continuous sheets, webs and similar forms of materials.

Continuous paper sheets are largely conventionally dried by passing them over serially arranged steam heated drying rolls, alternate ones of which are vertically displaced so that the drums are arranged in two vertically spaced decks. In the normal arrangement in such equipment the paper passes under one roll and over the next one so that heat is transferred by conduction from adjacent drying rolls to opposite sides of the paper to insure equal drying and thereby prevent curling. Such conventional drying systems have several disadvantages, particularly when operated at high speeds. As the paper passes over successive rolls, substantial portions of both faces of the sheet are in direct contact with the drying rolls. Moisture at and near the surface of the portions of the faces contacting the drying rolls is vaporized but cannot escape directly to the atmosphere because of the physical obstruction of the heating roll. As a result, the vapor pressure at the roll contacting face of the sheet increases, causing the water molecules to migrate toward the opposite exposed face of the sheet. Some of the water vapor will escape from the sheet through the exposed face; but, because the exposed face is relatively cool, many of the Water molecules migrating toward the exposed face will condense and remain in the sheet, retarding the drying process.

Escape of water vapor from the drying sheet is further retarded in such conventional equipment by felt or similar belts looped around the drying rolls and covering the sheet to minimize wrinkles in the sheet and to increase the heat transfer rate between the drying rolls and the sheet by pressing the sheet against the drying rolls. Little if any moisture is absorbed by or penetrates and escapes from these belts.

In the preferred embodiment of the present invention, a felt belt is used to press the sheet into contact only with selected drying rolls (preferably those in the lower deck) to prevent wrinkles and to obtain maximum conductive heating. By not employing the belt around the drying rolls in the upper deck, large areas of the sheet are always exposed to the ambient atmosphere, substantially increasing the ease with which moisture may escape from the sheet. In addition, in the present invention, radiant heaters are preferably located closely adjacent the exposed surfaces of the sheet and heated air is blown between the radiant heaters and the sheet to more rapidly dry it and to sweep away moisture evaporating from it. It has been found that this combination of radiant, conductive, and convective heating results in an unexpectedly large and surprising increase in drying efficiency in comparison to conventional equipment, permitting papermaking equipment to be run at increased speeds varying from f.p.m. (paperboard) to 3000 or more f.p.m. (newsprint).

In the preferred embodiment of this invention, the heated air is directed between the paper and the radiating surfaces by nozzles equal in length to and extending across the width of the sheet. Air flow through .the nozzles is preferably maintained at velocities of 1000 to 1500 f.p.m. relative to the velocity of the sheet being treated to cause turbulent flow in the zone between the moving sheet and the radiators as turbulent flow is substantially more effective in sweeping away evolved moisture than laminar flow. The combination of turbulent heated air moving at relatively high velocity over the sheet surface and the simultaneous application of radiant heat to the exposed surface of the sheet has a synergistic effect on the removal of moisture from the sheet, raising the drying rates of apparatus employing this combination of heat transfer mechanisms well beyond that which would be expected from a consideration of their additive effects.

The most pertinent prior art of which I am aware is my own British Patent 779,326 which discloses drying apparatus in which air is blown between the tops of rolls carrying wet web material and curved radiators for the sole purpose of eliminating vapor locks between the rolls and the radiators. Optimum air stream temperatures for vapor lock removal range from 100 to F. and the air flow is preferably laminar. Laminar air flow retards heat transfer from a relatively low temperature air stream; contributes little, if anything, to the drying action of the apparatus other than vapor removal; and, in fact, may cause substantial re-entry of water molecules into the sheet, reducing drying efficiency.

In the present invention the radiators employed to add radiant heat to the sheet are preferably maintained at a temperature of 550 F. or higher, and the drying air is introduced through the nozzles at temperatures preferably in the order of 250 F. to 500 F. and at velocities on the order of 1000 to 1500 f.p.m. relative to the velocity of the sheet to evaporate water from the sheet and to sweep the emerging water vapor away from its surface. By employing drying air and radiant heat having these temperatures and velocity parameters, the present invention achieves wholly unexpected and surprising increases in drying efficiencies, efiiciencies which would be impossible to obtain using my British patent disclosure.

Another advantage of my novel drying method and apparatus described above is that the addition of convection and radiant heating minimizes the non-uniformity in dry-ing caused by variations in the thickness of the sheet. Consequently, the formation of puckers is minimized, producing a sheet of higher quality.

From the foregoing, it will be apparent that one object of the present invention resides in the provision of improved methods and apparatus for drying continuous, moving sheets of material.

Another specific object of the present invention. resides in the provision of improved plural roll sheet drying apparatus having a substantially higher capacity than heretofore available apparatus of this type.

It is another specific object of the present invention to provide novel paper drying methods and apparatus which will minimize wrinkling and puckering of the paper.

Another object of the present invention resides in the provision of novel apparatus for drying continuous, moving sheets of material in which heat is transferred to the sheet by radiation and in which a stream of air is directed across the surface of the moving sheet to remove from adjacent the sheet moisture evolved from it.

It is yet another object of the present invention to provide novel plural roll apparatus for drying continuous, moving sheets of material including means for transferring heat to the material at a rate entirely independent of the tension on the material.

Still another specific object of the present invention resides in the provision of novel apparatus for drying continuous, moving sheets of material by radiation and conduction in which the heat input to the opposite sides of the material is correlated to prevent it from curling.

It is yet another specific object of the present invention to provide improved multi-roll apparatus for drying continuous, moving sheets of paper in which, to a significant extent, the moisture trapping felt belts heretofore em ployed to prevent the paper from wrinkling are eliminated.

Other objects and advantages of the present invention will become apparent from the following description of the preferred mode of carrying out the present invention, and examples thereof, and from the appended claims and accompanying drawings wherein:

FIGURE 1 is a partially diagrammatic front elevation, partly in section, of a drying apparatus embodying the principles of the present invention;

FIGURE 2 is a plan view of the apparatus illustrated in FIGURE 1; and

FIGURE 3 is an end elevation view of the apparatus illustrated in FIGURE 1.

Referring now to the drawing, FIGURE 1 illustrates a drier particularly adapted for drying a continuous, moving sheet of material 22. Drier 20 includes, generally, a plurality of internally heated drying rolls 2436 for heating sheet 22 by conduction, radiators 38 and 40 for applying radiant energy to sheet 22, and a ventilating system 42 for heating sheet 22 by convection and for removing from adjacent sheet 22 vapors evolved from it by the heat applied to it by the heated air, the drying rolls, and the radiators.

Drying rolls 24-36 may be of any conventional construction, such as the steam heated rolls illustrated in my British patent, for example. They are arranged in two vertically spaced apart decks indicated generally by reference characters 44 and 46 with the rolls 26, 30, and 34 in upper deck 44 located approximately midway between the drying rolls in lower deck 46. As shown in FIGURE 1, sheet 22 is guided onto the first drying roll 24 by a guide roller 48 and then moves around drying rolls 26, 28, 3t 32, 34, and 36 in that order, alternately passing between rolls in upper deck 44 and lower deck 46. Sheet 22 is guided from the last drying roll 36 by a guide roller 50.

A felt belt 52 is employed to press sheet 22 into contact with the drying rolls 24, 28, 32, and 36 in lower deck 46 to provide optimum conduction of heat from the drying rolls to sheet 22 and to prevent the formation of wrinkles in the sheet. Felt belt 52 is guided around the drying rolls in lower deck 46 by the guide rollers 48 and 50 discussed above and by pairs of guide rollers 54 and 56 located between adjacent rolls in the lower deck 46. Felt belt 52 is maintained under high tension in any suitable manner so that it will exert pressure in a direction normal to the sheet contacting surface portions of the drying rolls in lower deck 46.

Except for the novel arrangement of felt belt 52, that portion of applicants novel drier 20 described above is similar to the conventional multiroll drier commonly employed in the drying of paper. In a common method of manufacture of paper (and by the term paper is meant diverse products such as newsprint, paperboard, and the like), a mixture of water and fiber is continuously delivered onto a closely woven wire Fourdrinier conveyor. The water drains through the conveyor, forming a continuous mat of fibers on its upper side. After additional moisture is removed from the mat thus formed, as by suction boxes, the mat is passed through a multi-roll drier to complete the drying process.

As far as practicable, the rate at which the furnish or stock (typically consisting of 1-2% fiber and 9899% water) flows onto the conveyor is maintained constant so that the thickness of the sheet will be uniform. In actual practice of such prior methods it is impossible to achieve a high degree of uniformity and, as a result, what are known as wet streaks are present in the sheet when it reaches the multi-roll drier. The presence of wet streaks is undesirable since they dry more slowly than the remainder of the sheet which, as a result, shrinks to a greater extent than the wet streaks. Consequently, the wet streaks are not held tightly against the drying rolls and, therefore, tend to pucker or expand, lowering the quality of the finished product. The conventional multiroll drier tends to aggravate the formation of puckers and Wrinkles since the drying sheet is heated solely by conduction and the rate at which the drying rolls conduct heat to the sheet is dependent upon the tension of the sheet. Thus, in the conventional multi-roll drier, the dry streaks (the areas other than wet streaks) are the only portions of the sheet under tension and, therefore, dry at a faster rate than the wet streaks throughout the entire pass through the drier.

It is one of the novel features of the present invention that, notwithstanding the presence of wet streaks in the sheet entering drier 2i), non-uniform drying of the sheet is minimized and substantially eliminated. This is effected by utilizing, in addition to steam heated drying rolls 2436, heat transfer which is independent of the tension on sheet 22 and which adds heat to the wet streaks at a faster rate than to the dry streaks. The rate at which heat is transferred to a sheet of material by radiation or by convection is independent of the tension on the sheet and the novel drier 20 of the present invention employs both of these heat transfer mechanisms to provide substantially uniform drying of sheet 22.

Radiant energy is applied to sheet 22 by the radiators 38 and 40 referred to above. Radiators 38 and 40 may be of any desired construction; for example, that disclosed in copending application No. 64,965, filed October 25, 1960, by Horace L. Smith, In, for Paper Drying System, Apparatus and Method (now Patent No. 3,174,228). As is best shown in FIGURE 1, two radiators 38 are employed in association with each of the drying rolls 26, 30, and 34 in upper deck 44. The two radiators 38 employed with each of these rolls subtend substantially that portion of the associated drying roll contacted by the sheet of material 22 being dried; i.e., somewhat more than half of the roll surface. Radiators 38 are supported in any desired manner closely adjacent the surfaces of the associated drying rolls, the distance between the radiators and the drying rolls preferably being the minimum needed to permit sheet 22 to bereadily threaded around the drying rolls. Radiators 38 are surrounded by suitable reflectors indicated generally by reference character 58 so that the maximum portion of radiant energy emitted from the radiators will be directed onto sheet 22.

Two radiators 40 are mounted in any desired manner subjacent each of the drying rolls 26, 3t), and 34 in upper deck 44. Radiators 46 are separated from sheet 22 as it passes between the upper and lower decks of drying rolls 44 and 46 by guides 60 to prevent broke from contacting the radiators.

Radiators 38 and 40 are preferably maintained at a temperature on the order of 550 F. or higher by circulating through them a high boiling point organic liquid such as Aroclor 1248, a biphenyl manufactured by Monsanto Chemical Co. A preferred system for heating and circulating the heat transfer liquid is disclosed in copending application No. 237,817, filed November 15, 1962, by Horace L. Smith, Jr., for High Temperature Heating Appa- 5 ratus (now Patent No. 3,236,292), to which reference may be had if deemed necessary.

At a temperature of 550 F. radiators 38 and 40, the emitting surfaces of which have an emissivity coefficient of about 0.95, emit approximately 1,300 B.t.u.s of radiant energy per square foot per hour. As it requires approximately 1,000 B.t.u.s to evaporate one pound of water, each square foot of the radiators 38 and 40 will emit sufficient energy to evaporate approximately 1.3 pounds of water per hour from sheet 22. Therefore, in addition to promoting more uniform drying, radiators 38 and 40 evaporate substantial quantities of water from sheet 22, permitting the velocity of sheet 22 through the drier to be materially increased or, alternatively, permitting the number of drying rolls to be decreased. In either case thecapacity of a drier constructed in accordance with the present invention is substantially increased over that of a conventional multi-roll drier of equal size.

Preferably, as in the illustrated embodiment, radiant energy is applied to both sides of sheet 22 to equalize the heat input and thereby prevent the curling which would occur if the opposite sides of the sheet were unequally heated.

In the drying of continuous, moving sheets of material in multi-roll driers, the heat applied to the material by the drying rolls causes molecules of the liquid in the material to evaporate from the surfaces of the material which are not in contact with a drying roll or a felt and are therefore free or exposed. This forms a dry boundary layer in the material and a vaporous barrier layer adjacent its exposed surfaces. As the drying process continues, molecules of the liquid in the material migrate from the material through the dry boundary layer and escape from the material into the barrier layer. As the concentration of molecules in the barrier layer increases, these molecules diffuse toward areas of lower concentration. Since the dry boundary layer of the material is immediately adjacent the barrier layer, some of the diffusing molecules will return to the material, retarding the drying process. To remove the liquid from the barrier layer and hasten the drying process by preventing the molecules in this layer from returning to the boundary layer, the ventilating system identified by reference character 42 is employed.

As is best shown in FIGURE 2, ventilating system 42 includes a blower 62 driven by a motor 64 which directs air through a suitable air heater 66 such as that shown in copending application No. 271,801 filed April 9, 1963 by Horace L. Smith, Ir., for Dryers (now Patent No. 3,208,158), where the air is heated to a temperature above the boiling point of the liquid being evaporated from sheet 22 and below the temperature of radiators 38 and 40. For paper drying the air is preferably heated to a temperature in the range of 250-500 F. From heater 66, the air passes into an inlet air manifold 68 which conveys the hot air downwardly into a plurality of plenums 70 (FIGURE 1) from which the air is discharged through nozzles 72 as shown by the arrows in FIGURE 1 between the drying rolls 26, 30, and 34 in upper deck 44 and the radiators 38 surrounding these rolls, preferably at a velocity in the range of 10004500 feet per minute greater than the speed at which the web is moving. In relation to the movement of the paper, part of the air flow is concurrent and part countercurrent; and, consequently, the relative velocity between the air stream and sheet 22 will be different on opposite sides of nozzles 72 at each drum as the air will be flowing in the direction of web movement on one side of each nozzle and opposite to the direction of web movement on the other side of the nozzle. Nozzles 72 are preferably at least as long as the width of sheet 22 so that the heated air will be distributed across its entire surface.

The heated air flows upwardly between the radiators and sheet 22, through outlet plenums 74 (which have inlets 76 located between the two radiators 38 associated with 6 each of the drying rolls in upper deck 44), and into outlet manifold 78 which recirculates the air to blower 62.

The heated air sweeps across sheet 22 as it travels over the drying rolls 26, 30, and 34 in upper deck 44, carrying away the vapor in the barrier layer adjacent its surface and thereby preventing the molecules in the barrier layer from returning to sheet 22 as they would otherwise do. In addition, the heated air heats sheet 22 by convection, further hastening'the drying process by increasing the rate at which vapor is evolved from sheet 22 and increasing the capacity of drier 20 over that of a conventional multiroll drier of comparable size.

At the velocities and temperatures described above, the flow of the heated air stream between radiators 38 and the associated rolls in upper deck 44 is highly turbulent, the flow condition most effective in removing evolved vapors from adjacent sheet 22 and in transferring heat to it by convection. Preferably, the turbulence of the flowing air is increased by providing the inner surfaces of radiators 38 with undulating or transversely rippled formations or by fixing spaced fins to these surfaces. To further increase the turbulence of the flowing air, a coarse mesh, open weave belt may be substituted for felt belt 52. I

As sheet 22 passes through drier 20, it reaches a stage of dryness corresponding approximately to the condition of fiber saturation in which the free water between the fibers has been evaporated. At this point, which is termed the falling rate portion of the drying cycle, the drying rate begins to decrease. The dry streaks reach the falling rate part of the drying cycle considerably sooner than the wet streaks and, after reaching this stage, dry at a substantially lower rate than the wet streaks which therefore continue to absorb heat from radiators 3 8 and from the heated air circulated between the radiators and the sheet at a maximum rate. As a result, the dry streaks dry slowly and the wet streaks dry considerably more rapidly and the sheet as a whole dries at a substantially more uniform rate than has heretofore been possible, minimizing the formation of wrinkles and puckers in the sheet.

Adjacent the outlet end of drier 20, where sheet 22 approaches a substantially dry state, the temperature of radiators 38 and the temperature of the heated air discharged through nozzles 72 may be decreased to lower the rate at which heat is transferred to sheet 22 to protect it from overheating.

Escape of the evolved vapor from the sheet in a conventional rnulti-roll drier is inhibited by the fact that felt belts are employed to press the sheet against the drying rollers in the upper deck as well as in the lower deck, an arrangement which has heretofore been thought to be necessary to prevent wrinkles in the paper. As a result, the major portions of both sides of the sheet are either covered by the felt belt or in contact with the drying rollers; and, as a result, there is only limited area exposed surface through which the evaporated liquid may escape from the sheet.

In the present invention, in contrast, removal of moisture from sheet 22 is enhanced by the fact that sheet 22 is not covered with a felt belt as it passes over the rollers 26, 30, and 34 in upper deck 44. This provides considerably more exposed surface from which the evaporated moisture may escape from the sheet than do the conven tional prior art driers. Surprisingly, it has been found that the elimination of the felt belt from the upper deck rollers 26, 30, and 34 has substantially no adverse effect on preventing the formation of wrinkles and puckers in sheet 22. Elimination of the felt belt around the upper deck rollers 26, 30, and 34, in addition, makes it possible to advantageously employ radiant heaters in combination with a multi-roll type drier in contrast to the conventional arrangements heretofore employed in which such energy would, of course, be absorbed by the felt belts.

In most instances, it will be desirable to retain a small percentage of the liquid in the dried .sheet 22. For some types of paper, for example, the dried product should have a moisture content on the order of In the novel drier 20 of the present invention, the moisture content of the dried sheet 22 may be accurately and easily controlled by regulating the relative humidity of the drying air discharged through nozzles 72. For this purpose, an exhaust air duct 80 and a make-up air duct 82 are provided in exhaust manifold 78 and inlet manifold 68, respectively. Flow through exhaust duct 80 and make-up air duct 82 is regulated by valves 84 and 86 disposed in ducts 80 and 82, respectively. Valves 84 and 86 may be adjusted manually or may be automatically operated by the automatic humidity control system disclosed in copending application No. 271,801 filed April 9, 1963 by Horace L. Smith, Jr., for Dryers (now Patent No. 3,208,158),

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

\Vhat is claimed and desired to be secured by Letters Patent is:

1. Apparatus for heat treating a continuous, moving sheet of material, comprising:

(a) a plurality of substantially horizontally disposed drying rolls alternately located in first and second, vertically spaced apart decks and adapted to have a sheet of material contacting, respectively, their upper and lower surface portions, all of said rolls being internally heated;

(b) belt means for holding said sheet material against the rolls in one of said decks only, the other of said decks being entirely free of such 'belt means to permit volatiles evolved from the material being dried to escape freely from adjacent the surface of said material; and

(c) radiant heater means for applying radiant energy directly to the exposed surface of said sheet only in the deck which is free of belt means .so that said radiant energy is transferred with maximum efficiency from said heater means to said material;

(d) whereby there are drying rolls free of said belt means and with external heater means therearound to transfer radiant energy from said heater means to said material in sufficiently large amounts to significantly increase the rate at which said material is dried and yet belt means pressing said material against a sufficient number of drying rolls to prevent the formation of wrinkles in said material and to insure a heat conductive relationship between the material and the drying rolls.

2. Apparatus for heat treating a continuous, moving,

sheet of material, comprising:

(a) a plurality of substantially horizontally disposed drying rolls alternately located in first and second vertically spaced apart decks, all of said rolls being internally heated;

(b) belt means for holding said sheet material against the rolls in one of said decks, the other of said decks being entirely free of such belt means to permit volatiles evolved from the material being dried to escape freely from adjacent the surface of said material;

(c) radiant heater means around the internally heated drying rolls only in the other of said decks which is free of belt means for applying radiant energy directly to the exposed surface of said sheet in said other deck so that said radiant energy is transferred with maximum efiiciency from said heater means to said material;

((1) whereby there are drying rolls free of said belt means and with external heater means therearound to transfer radiant energy from said heater means to said material in sufficiently large amounts to significantly increase the rate at which said material is dried and yet belt means pressing said material against a sufficient number of drying rolls to prevent the formation of wrinkles in said material and to insure a heat conductive relationship between the material and the drying rolls;

(e) air supply means for introducing streams of air between the radiant heater means and the drying rolls of said other deck at a velocity sufficiently high to remove from adjacent said sheet vapors evolved therefrom, said air supply means being associated only with the rolls of said other deck, and said air supply means including a plurality of inlet plenums located adjacent and spanning the length of the drying rolls in said other deck, means forming in each plenum at least one nozzle communicating with the interior of the plenum and having an outlet closely adjacent one of said drying rolls; and

(f) means for exhausting the vapor laden air streams from between said sheet material and said radiant heater means.

3. Apparatus as defined in claim 2, together with:

(a) a supply manifold in fluid communication with said inlet plenums;

(b) an air heater with its outlet communicating with the interior of said manifold; and

(c) a blower with its outlet communicating with the inlet to the air heater to force air seriatim through the air heater and the inlet manifold, .into the inlet plenums, and through the nozzles communicating therewith.

4. Apparatus as defined in claim 3:

(a) wherein said exhaust means comprises exhaust plenums above and spanning each of the drying rolls in said other deck, said plenums having inlet openlngs in the bottom thereof;

(b) an exhaust manifold in fluid communication with said exhaust plenums and the inlet of said blower, whereby said air supply means and said exhaust means constitute a closed system providing for recirculation of said air;

(0) an exhaust duct communicating with said closed system and open at one end to the atmosphere;

((1) a makeup air duct communicating with said closed system and open at one end to the atmosphere; and

(e) selectively adjustable valves in the exhaust and makeup air ducts for controlling the discharge of vapor laden air from and the entry of fresh air into said system.

5. Apparatus for heat treating a continuous, moving sheet of material, comprising:

(a) a plurality of substantially horizontally disposed drying rolls alternately located in first and second, vertically spaced apart decks and adapted to have a sheet of material contacting, respectively, their upper and lower surface portions;

(b) belt means for holding said sheet material against the rolls in one of said decks only, the other of said decks being free of felts;

(c) radiant heater means for applying radiant energy to the exposed surface of said sheet only in the other of said decks;

(d) means for introducing a stream of gas between said radiant heater means and the sheet material on the rolls in said other deck and directing said gas around said rolls adjacent said sheet material at a velocity sufiiciently high to remove from adjacent said sheet vapor evolved therefrom; and

(e) means for exhausting the vapor laden gaseous stream from between said sheet material and said heater means;

(f) the means for introducing said stream of gas between said heater means and said sheet material comprising:

(g) means forming at least one plenum chamber located between adjacent rolls in said second deck; and

(h) means forming a pair of nozzles in said plenum chamber, said nozzles being in fluid communication with the interior of said chamber and each of said nozzles being directed toward the adjacent one of the drying rolls between which the associated plenum chamber is located, said nozzles having outlets closely adjacent and spanning the length of said drying rolls.

6. Apparatus for heat treating a continuous, moving sheet of material, comprising:

(a) a plurality of substantially horizontally disposed drying rolls, alternately located in first and second, vertically spaced apart decks and adapted to have a sheet of material contacting, respectively, their upper and lower surface portions, all of said rolls being internally heated;

(b), belt means for holding said sheet material against the rolls in one of said decks only, the other of said decks being'entirely free of such belt means to permit volatiles evolved from the material being dried to escape freely from adjacent thepsurface of said material;

() radiant heater means for applying radiant energy directly to the exposed surface of said sheet only in the deck which is free of belt mean-s so that said radiant energy is transferred with maximum efliciency from said heaters to said material;

(d) whereby there are drying rolls free of said belt means and with external heater means therearound 10 to transfer radiant energy from said heater means to said material in sufficiently large amounts to significantly increase the rate at which said material is dried and yet belt means pressing said material against a suflicient number of drying rolls to prevent the formation of wrinkles in said material and to insure a heat conductive relationship between the material and the drying rolls;

(e) means for introducing a stream of gas between said radiant heater means and the sheet material on the rolls only in the deck which is free of belt means and for directing said gas around said rolls adjacent said sheet material at a velocity sufficiently high to remove from adjacent said sheet vapor evolved therefrom; and

(f) means for exhausting the vapor laden gaseous stream from between said sheet material and said radiant heater means.

References Cited by the Examiner UNITED STATES PATENTS FREDERICK L. MATTESON, JR., Primary Examiner. A. D. HERRMANN, Assistant Examiner. 

1. APPARATUS FOR HEAT TREATING A CONTINUOUS, MOVING SHEET OF MATERIAL, COMPRISING: (A) A PLURALITY OF SUBSTANTIALLY HORIZONTALLY DISPOSED DRYING ROLLS ALTERNATELY LOCATED IN FIRST AND SECOND, VERTICALLY SPACED APART DECKS AND ADAPTED TO HAVE A SHEET OF MATERIAL CONTACTING, RESPECTIVELY, THEIR UPPER AND LOWER SURFACE PORTIONS, ALL OF SAID ROLLS BEING INTERNALLY HEATED; (B) BELT MEANS FOR HOLDING SAID SHEET MATERIAL AGAINST THE ROLLS IN ONE OF SAID DECKS ONLY, THE OTHER OF SAID DECKS BEING ENTIRELY FREE OF SUCH BELT MEANS TO PERMIT VOLATILES EVOLVED FRO THE MATERIAL BEING DRIED TO ESCAPE FREELY FROM ADJACENT THE SURFACE OF SAID MATERIAL: AND (C) RADIANT HEATER MEANS FOR APPLYING RADIANT ENERGY DIRECTLY TO THE EXPOSED SURFACE OF SAID SHEET ONLY IN THE DECK WHICH IS FREE OF BELT MEANS SO THAT SAID RADIANT ENERGY IS TRANSFERRED WITH MAXIMUM EFFICIENCY FROM SAID HEATER MEANS TO SAID MATERIAL; (D) WHEREBY THERE ARE DRYING ROLLS FREE OF SAID BELT MEANS AND WITH EXTERNAL HEATER MEANS THEREAROUND TO TRANSFER RADIANT ENERGY FROM SAID HEATER MEANS TO SAID MATERIAL IN SUFFICIENTLY LARGE AMOUNTS TO SIGNIFICANTLY INCREASE THE RATE AT WHICH SAID MATERIAL IS DRIED AND YET BELT MEANS PRESSING SAID MATERIAL AGAINST A SUFFICIENT NUMBER OF DRYING ROLLS TO PREVENT THE FORMATION OF WRINKLES IN SAID MATERIAL AND TO INSURE A HEAT CONDUCTIVE RELATIONSHIP BETWEEN THE MATERIAL AND THE DRYING ROLLS. 